Photonic integrated circuits (PIC) are semiconductor chips that include several optoelectronic components (e.g. semiconductor lasers, detectors, waveguides, FET devices, etc.). Such chips can be fabricated using various techniques that have been developed for the individual components. However, because each different component (e.g. a laser and a waveguide) requires a different layer structure, that is a stack of several layers having different thicknesses and compositions, the fabrication of PIC's using these known different techniques requires many processing and growth steps.
More advanced techniques have been disclosed in the literature that make it possible to grow the layers for the different components over the surface of a substrate in a single run. This can be done by controlling the lateral variations in the growth rate over the surface of the substrate, thereby to change the bandgap of the quantum wells in a controllable way laterally over the surface of the substrate. These advanced techniques include selective growth, shadow masked growth and non-planar growth using Metal Organic Chemical Vapour Deposition (MOCVD) growth in a reactor.
For growing high quality layers, the right growth conditions are chosen so as to obtain the best layers. The growth parameters include the temperature, pressure, gas flow.
Using the known techniques provides chips including several devices that consist each of a stack of several layers having different thicknesses and compositions. The composition within a few atomic layers can be changed by changing the gas that is switched to the MOCVD reactor.
As noted above, the growth rate can be controlled for each device over the surface of the substrate and this results in a complete integrated chip including devices in which the active layers are not lying at the same height. Such a structure has some disadvantages in that the coupling between different devices (e.g. a laser and a semiconductor waveguide) is not perfect and the overall surface is not planar.